1. Field of the Invention.
The present invention relates generally to a method for the preparation of organopolysiloxane, and more particularly to a method for the preparation of an organopolysiloxane which carries 2 or 3 diorganohydrogensiloxy groups at one and only one molecular chain terminal.
2. Description of the Prior Art.
Organopolysiloxane carrying the diorganohydrogensiloxy group at only a single molecular chain terminal is employed as starting material for the preparation of organopolysiloxane carrying various types of organofunctional groups at the one molecular chain terminal. The former is also employed as an additive for improving or modifying the physical properties of organic resins.
Organopolysiloxane carrying the diorganohydrogensiloxy group at only one end of the molecular chain has heretofore been prepared by the following methods:
an ionic equilibration polymerization reaction in the presence of strong acid catalyst of a mixture of diorganohydrogensiloxy-containing organopolysiloxane and diorganohydrogensiloxy-free organopolysiloxane; and PA1 the ring-opening polymerization of hexaorganocyclotrisiloxane using alkyllithium or lithium silanolate, etc., as initiator, followed by termination of the polymerization with dimethylchlorosilane.
However, the organopolysiloxane afforded by the former method is obtained as a mixture of: (i) organopolysiloxane carrying diorganohydrogensiloxy only at one end of the molecular chain; (ii) organopolysiloxane carrying diorganohydrogensiloxy at both ends of the molecular chain; and (iii) organopolysiloxane lacking diorganohydrogensiloxy at the molecular chain terminals.
On the other hand, the latter method can produce only organopolysiloxane carrying a single diorganohydrogensiloxy group at one end of the molecular chain.
In Japanese Patent Application Number 1-207631 [207,631/89], the present inventors proposed organopolysiloxane carrying 2 diorganohydrogensiloxy groups at only one end of the molecular chain as well as a method for the preparation of same.
However, this preparative method suffers from a low yield of the organopolysiloxane carrying 2 diorganohydrogensiloxy groups at only one end of the molecular chain due to the instability of an intermediate (an organopolysiloxane having 2 hydroxyl groups at only one end of the molecular chain). Furthermore, this preparative method cannot provide organopolysiloxane carrying 3 diorganohydrogensiloxy groups at the one molecular chain terminal.